In the past, conventional springs mounted in a sealing jacket or casing have often lost their resilient sealing capabilities when subjected to repeated use under extreme pressures and temperatures. It is believed that such failures have been caused by poor construction features of the spring/cover combination whereby the forward flexing ends of the spring are held in fixed longitudinal position by the overlapping forward lips of the cover while the central spring leg moves back and forth in the inner cavity of the cover to accomodate the lateral flexing of the spring. Such prior art structure results in bad performance by both the spring and the cover or jacket. Such prior art seal/cover combinations have therefore failed to provide continuous reliable sealing along a smooth evenly loaded sealing surface over extended periods of time.